This invention relates to a laminated-type photosensitive member with at least a charge generating layer and a charge transporting layer on an electrically conductive substrate. In particular, the photosensitive member in improved in repetition-use properties and life of the charge transporting layer.
In general electrophotography, many methods for forming copied images are known. For example, the surface of a photosensitive member is charged and irradiated to form electrostatic latent images thereon, the electrostatic latent images are developed to visible images by a developer, and then the developed images are fixed directly onto the photosensitive member (this method is referred to as a direct method). Alternatively, developed electrostatic latent images on a photosensitive member which are made visible by a developer are transferred to a copying paper and then, the transferred images are fixed on the copying paper (this method is referred to as a powder transferring method). In another method, electrostatic latent images on a photosensitive member are transferred onto a copying paper, the transferred electrostatic latent images are developed by a developer and then fixed on the copying paper (referred to as an electrostatic latent image transferring method).
With respect to photoconductive materials conventionally used for forming a photosensitive layer, inorganic photoconductive materials such as selenium, cadnium sulfide, zinc oxide and the like are known.
These photoconductive materials have many advantages, such as ability to be charged to an adequate potential, low loss of electrical charges in the dark, a rapid dissipation of electrical charges with irradiation of light and the like. However, they have disadvantages. For example, a photosensitive member based on selenium is difficult to produce, has high production costs and difficult to handle due to inadequate resistivity to heat or mechanical impact. A photosensitive member based on cadmium sulfide has defects such as its unstable sensitivity in a highly humid environmental and loss of stability with time because of the deterioration of dyestuffs, added as a sensitizer, by corona charge and fading with exposure.
Many kinds of organic photoconductive materials such as polyvinylcarbazole and so on have been proposed. These organic photoconductive materials have superior film forming properties, are light in weight, etc., but inferior in sensitivity, durability and environmental stability compared to the aforementioned inorganic photoconductive materials.
In order to overcome the above mentioned problems, current researches and developments have proposed that the functions of charge generation and charge transportion in a photosensitive layer are divided to form a function-devided photosensitive member of a laminated type in which a charge generating layer and a charge transporting layer are laminated on an electrically conductive substrate, such as aluminium, copper or the like.
Such a function-devided photosensitive member of a laminated type is very high in productivity and cheap in production cost because it can be prepared generally by a coating method. Further, the wavelength region sensitive to light can be controlled freely by the adequate selection of a charge generating material. Therefore, the function-devided photosensitive member of the laminated type has been used widely in recent years.
It is necessary that the basic performances requisite for a photosensitive member, such as charge keeping properties, high sensitivity, repetition stability, resistance to break down, resistance to wearing, durability, resistance to humidity, transferring properties, cleaning properties, preservation properties and the like, are provided for the laminated-type photosensitive member. As the laminated type photosensitive member is applied to a laser printer or the like, higher reliability to copied images and higher repetition stability are required than before.
Therefore, a charge transporting layer is formed usually at the surface side of a photosensitive member in consideration of the durability with respect to toner cleaning of the surface of the photosensitive member after toner transferring process and the influences of surface injury and irregular layer-thickness on copied images.
However, such a photosensitive member with a charge transporting layer at the surface side has problems as before, such as irregular layer-thickness of the photosensitive member, cleaning failure of the surface of the photosensitive member, ununiform density of copied images resulted from degradation caused by humidity or ozone, and the like. When a copy process is repeated several hundreds of times continuously, there arise problems such as the shades in copied images, blurred copied images or the like.
In particular, the problems as above mentioned are remarkable in the case where a photosensitive member is applied to a laser printer which requires high reliability to copied images and repetition stability. Accordingly, a photosensitive member which can be applied to such a laser printer without such problems has been desired.
The problems as above mentioned are caused by degradation influenced by circumstances of ozone which are formed in continually repeated corona-charge processes of a charge transporting layer. Therefore, in order to prevent the degradation, gasses, such as ozone and the like, in the corona-charger neighborhood are exhausted mechanically. This mechanical means cannot overcome the problems completely.
In particular, when a photosensitive member is charged negatively, active gasses, such as ozone, NO.sub.x and the like are liable to generate by corona-discharges in a great amount and the photosensitive member is much influenced adversely by their gasses.
Accordingly, charge-transporting materials of electron-donating type and resins of charge transporting layers are much deteriorated, resulting in the defects of copied images, such as ununiform copied images and blurred copied images and the like, the lowering of the surface potential at the repeated uses and the lowering of the density of copied images.
Moreover, a coating solution for the preparation of a photosensitive member is influenced by light, acidic materials to arise such deteriorations as increase of viscosity, yellowing or the like.
The inventions in which a nitrogen-containing material is contained in a photosensitive layer of a photosensitive member for electrophotography are disclosed in Japanese laid-open Nos sho 63-4238, 63-73256, 63-18355 and 57-122444. But, the nitrogen-containing material is completely different in the chemical structure from that of the present invention which is going to be disclosed below.